


Behind Closed Doors

by QuintessenceA



Category: Undertale (Video Game)
Genre: Accidental Voyeurism, Angst, Begging, Crying, Ecto-Genitalia (Undertale), Guilt, M/M, Painful Sex, Plot What Plot/Porn Without Plot, Rape, Sanster
Language: English
Status: In-Progress
Published: 2020-10-18
Updated: 2021-03-03
Packaged: 2021-03-09 04:15:18
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 2
Words: 7,122
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27078661
Author URL: https://archiveofourown.org/users/QuintessenceA/pseuds/QuintessenceA
Summary: What if a regular, kind Gaster accidentally stumbled upon another Gaster doing awful, terrible, unforgivable things to their Sans?And ...what if ...he liked what he saw?
Relationships: W. D. Gaster/Sans
Comments: 13
Kudos: 66





	1. Chapter 1

**Author's Note:**

> (Content warnings for pure rape. Nothing dubious about it, Sans is fucked over pretty harshly)
> 
> I've been thinking about this all day, and hot damn it's about time I posted some Sanster. I hope you all enjoy reading this as much as I enjoyed writing it!
> 
> Inspired by Twitter.com/K8Maybe/status/1317283709003890688
> 
> Thank you for this tasty idea! I feel positively wicked now :)

Everything was set up to be a routine day in the Labs. Sans was catching up on some routine paperwork in one of the lower labs while Gaster himself was on Universal Camera duty. Not that he minded, of course. It was actually quite enjoyable to set the machine to search for random universes, and he was always interested in finding ones that were worth documenting as anomalies.

And, rarely, ones that were worth visiting.

He'd only been watching for around twenty minutes when the static on the display screen began to clear, showing the interior of the lower levels of the Labs. That was interesting. The machine's Active AU Viewer camera tended to land where the focus of the world's "story" takes place, and that was usually around Snowdin or up on the surface. 

Using the joystick, Gaster moved the viewer around as he searched for inhabitants. It wasn't truly there, of course, it only existed as a representation of a camera, partially out of sync with the reality it viewed but lined up enough to see and hear things that were happening, for lack of a better term, "now". 

The Labs were strangely quiet, no interns running tasks, no sign of himself, or Alphys, or anyone. He dropped through the floor to a lower level, and headed down the first corridor he saw. Halfway down the hallway, a closed door caught his eye, though he couldn't say why. 

These were all just regular exam rooms, and this door looked no different from the rest, but Gaster stopped anyway, wondering for a moment what it was that made him pause before he gave up and decided to phase the camera through the door. As he'd thought, it was a typical room of its type, with a moderate sized examination table in the center of the room. But… sitting on the table… was Sans.

But not Sans like he knows. For one, he was bareboned, but that wasn't the only problem.

He looked… scared. Hopeless.

Fury instantly coursed through Gaster. Was he injured?Had someone HURT Sans?! Who would DARE?? 

Angrily, Gaster grabbed his pen, making a record of this universe's coordinates as he vowed to find the culprit. Sans was a good friend, a fantastic apprentice and all around wonderful person! What sort of wicked creature would DO this?

He got his answer a moment later as the door opened, and Sans flinched backwards as a version of Gaster himself entered. The other's eyes swept the room and its occupant, his expression entirely devoid of anything resembling empathy or compassion for the poor monster in front of him.

Gaster faltered in his writing. Had he gotten the situation wrong? Maybe… Sans was ill? Was this some sort of examination?

"Are you ready, 01?" 

01?

Sans didn't reply other than to hurriedly move to lie prone on the table. And then he did something completely unexpected.

Sans summoned his Soul. 

It floated before him, pulsing with soft light as he gently cradled it behind the protective cage of his phalanges. Then, with trembling hands, he offered it out.

What… what sort of procedure was this?

Shocked, Gaster could only watch as the other Doctor callously plucked Sans's Soul from his shaking fingers before moving to the foot of the table. Sans then laid his hands down by his sides, fingers tightly gripping the edge as his body shook with his continued trembling. 

"Very good," the other Doctor said, and a larger shudder ran through Sans at the words. The Doctor saw, and his smile widened with something Gaster could only identify as sadistic glee.

Gaster was aghast. This man was enjoying Sans's fear!

His horror only grew as the Doctor began to run his thumbs across the surface of Sans's Soul. From the table, Sans made a choked sound, and magic began to seep from his bones, dripping like sweat from his skull and coalescing obscenely in his pelvic cradle. Gaster couldn't look away, his own Soul beating like a drum as he watched Sans struggle.

"Do not fight me," the Doctor admonished lightly. "You're only making this harder on yourself."

Sans closed his eyes, and gave a small, jerky nod. As the Doctor continued to touch -no, _fondle_ \- the Soul, Sans started to pant lightly, and his mouth fell open, revealing his summoned tongue. Gaster leaned forward in his seat, his mouth going dry. 

"More," the Doctor commanded, pressing his fingers roughly into the surface of the Soul.

Sans cried out, and with a crackling snap the swirling magic in his pelvis solidified, forming a feminine structure. He started to shake his head, pulling his knees up to protect himself.

"no, no," Sans whispered plaintively. "i can't, please."

Gaster watched, scarcely breathing, as the other roughly grabbed Sans's ankle and pulled him to the edge of the table, demanding, "You can, and you will."

The Doctor still held Sans's Soul and, with a wicked grin unlike anything Gaster had known his face was capable of making, brought it to his mouth. His violet tongue, only a shade darker than Gaster's own, slithered out from between his teeth. Gaster couldn't stop his mouth from salivating as he watched the other drag his tongue across the surface of the Soul in a long, slick glide.

Sans gave a short moan, the sound echoing in the small room. When the Doctor finally dropped his ankle, Sans simply let it fall, leaving himself spread open to the Doctor before him.

Gaster knew he needed to stop staring, he needed to intervene, to do anything but watch where this was going! This was wrong!

…and yet he did nothing as he saw tears well up in the corners of Sans's sockets, spilling over to drip in long blue streaks down the side of his face. Sans was… disturbingly beautiful like that.

When the Doctor moved to undo his pants, Gaster mimicked the motion, sliding his own hand under his waistband. In tandem with the other on screen, Gaster squeezed his already hard member, feeling dimly sick with himself but unable to look away.

He shuddered with anticipation as the other grabbed Sans's hips, lining him up with his own, and began to rub his length along Sans's folds. Blue slick smeared along purple magic, drawn out by the Doctor's attention to his Soul. Precum dripped down through Gaster's own fingers, bringing a pleasant glide to his own increasingly frantic movements. It felt too good, and Gaster knew it wouldn't last.

"Get on with it," Gaster hissed at the screen.

As if he'd heard, the other Doctor's hips shifted forward, closing the space between himself and his hapless subject. He paused once more, but before Gaster could become frustrated again he suddenly snapped the rest of the way forward, burying himself harshly into the glistening blue magic. 

Sans cried out, clutching the sides of the table as his body arched up, instinctively trying to pull away from the sudden intrusion. The sound quickly shifted to hoarse, gasping whimpers as the Doctor set a brutal pace, pistoning in and out while Sans cried under him.

Gaster shifted his attention away from where the two were joined, to see Sans's Soul continuing to well with silver magic as it beat frantically in the other's grip. 

The Doctor's thrusting grew even harsher as he started to loose himself, chasing his climax. As Gaster watched, his fingers began to tighten around the Soul, and Sans's voice rose in pitch as the core of his being was mercilessly squeezed. 

Gaster was entranced by the expression on Sans's face. Afraid. Pained.

_Overwhelmed._

It was too much, and Gaster pressed his wrist to his mouth, muffling his cry as he came, shuddering into his hand while he stared at his poor assistant on the screen.

The other Doctor was right behind him, sinking himself deeply into Sans one final time before stilling with a groan of pure satisfaction. When he was done, he pulled out, releasing the Soul.

It wavered in the air a moment before unsteadily drifting back to Sans like an injured creature seeking its den. His ordeal over, Sans rolled onto his side, curling into a ball while the Doctor readjusted his pants.

"Alright, 01. You may return to your cell now."

Any reply Sans might have made was lost when Gaster hit the power to the machine, ashamed and disgusted with himself. How… how could he have done that? What was wrong with him? 

And why, for the love of all the Stars, had it felt so good?

~~~

The things Gaster had witnessed on the screen that day haunted him. It upset him. It horrified him that somewhere a version of him did such repulsive things. But worse of all, it had awoken a hunger that Gaster had never even imagined could be lurking within his Soul. 

He wanted it to be him. To have Sans like that, frightened beneath him, unable to stop him as he took what he wanted from Sans's body.

It only got worse when he realized… he could do it. Sans would never expect it. It would be easy. It would be wrong, but Stars, he wanted it more than he'd ever wanted anything else in his life.

It was these thoughts that accompanied Gaster as he walked into the lab where Sans was working. 

"heya, doc," Sans said, grinning up at him from where he leaned back against a countertop, scribbling notes onto a clipboard in his hands. His writing stopped as he caught sight of Gaster's face. "you look thoughtful. something on your mind?"

"I… I found another AU," Gaster said, shutting the door behind him and moving closer.

Sans's smile faltered for a moment at whatever expression Gaster was showing, and his sockets shifted to concern. "oh? didn't go so good, huh? one of the bad ones?"

Gaster ignored the question, taking another step forward to stand directly in front of him. "I- I want to try something."

"yeah?" Sans asked, drawing his clipboard to his chest. "sure, but, uh, would y'mind stepping back a bit?"

Sans was beginning to look nervous, but Gaster wanted more than that. 

Lashing out, Gaster knocked the clipboard from his grip, and with a gasp of surprise, Sans let go to watch it clatter noisily against the tile floor. While he was distracted, Gaster's hand shot out to grab Sans's wrist. His sockets went wide, and _oh, yes,_ there was that fear.

"i- i suppose you n-need a hand with something?" Sans squeaked, feebly trying to pull his arm free. "d- doctor Gaster?"

It was close, but it wasn't enough. Gaster began to squeeze, and Sans pulled harder as the pressure grew, inching closer and closer to the point of causing real damage, until Sans cried out, "Gaster! stop! what are you doing?!"

"Yesss," Gaster said, drawing the word out as he drank in that expression on Sans's face. Terror was amazing on him. He stopped squeezing, but didn't let go.

"wh-whatever this is, we can talk about it!" Sans pleaded, grabbing Gaster's arm with his free hand. "please, Gaster, l-let me go!"

"No." Gaster leaned in further, to nuzzle the side of Sans's face with his own. Sans pulled back, his spine bending against the counter top.

"please," Sans tried again, letting go of his arm to uselessly push one handed against his chest. "Gaster, please."

"Ahh… that way you say my name," Gaster purred, and Sans shuddered against him.

Gaster loved it. He wanted more.

Without giving him any warning, Gaster grabbed Sans's shoulder, twisting him around before swiftly bending him over the counter. Quickly, he summoned a pair of hand constructs to take Sans's wrists, pinning them down in front of him. Sans fought against it, but his physical strength was no match for Gaster's magic. His hands now free, Gaster rucked Sans's labcoat up between them before slipping a hand into the front of Sans's shorts to roughly rub against his pubic symphysis. 

"what?! don't! no! d-mmm!" Sans cried out and Gaster cut him off, wrapping his other hand around his mouth, enjoying the feel of Sans's increasingly panicked breath against his fingers. The bone started to grow warm as Gaster worked his pelvis, and Gaster let out a pleased moan at the way Sans struggled against him, squirming and bucking against his hips as he tried to break free. 

"Form something for me," Gaster commanded, and Sans shook his head fiercely, closing his sockets as he refused.

"Fine," Gaster said, bringing his face down to whisper the words against the side of Sans's skull. "I know how to fix this."

Pulling his hand free from the shorts, he reached up to press it against the side of Sans's ribcage. A flicker of intent, and he began to draw out his Soul. As soon as Sans realized what was happening, his eyes shot open and he twisted his head to stare at Gaster, his eyelights shrunk to tiny, shaking points of light in his wide, terrified sockets.

Whatever Sans saw in Gasters eyes was enough to make him fight in earnest, his movements turning desperate in a way that had Gaster's magic singing in delight. 

"nnnn! _nnnn!_ " He cried against Gaster's hand.

His Soul resisted, but Gaster only pulled harder. When it finally popped free from Sans's chest with a snap, Sans jerked hard enough that his face slipped free of Gaster's hold. Gaster only moved his hand to wrap his fingers around Sans's lovely, delicate throat instead.

"p-please don't!" Sans shouted as Gaster brought the Soul closer to his face, admiring its beauty. 

It fluttered against his fingers like a terrified bird, waves of Sans's fear and revulsion battering Gaster with every beat. It was incredible. Licking his teeth, Gaster brought it to his mouth.

_-A dark voice whispered in the back of his mind, asking what it would feel like to sink his teeth into it, how the shuddering would feel sliding down his throat-_

Sans must have felt some of that, as his pleading ratcheted up several notches, tears finally starting to form in the corners of his sockets. 

"no, nonono," he begged, the words thrumming pleasantly against the fingers still wrapped around Sans's throat. "Gaster, Gaster please! stop- no, Ga- _ahhhh!_ "

Sans's cry turned to a helpless moan as Gaster only ran his tongue along the pale construct, just as he'd seen the other do before. He did it again, this time pushing his intent into it, needing, demanding. 

It pulsed against his fingers, and Gaster felt a sharp rush of shame from the Soul as Sans's magic was forced into being.

"Very good," Gaster praised. He could feel the turmoil of Sans's emotions as the warmth of praise he so craved was warped by Gaster's twisted desire.

 _Good, good, good,_ Gaster told the Soul as he worked to lather it with attention. Sans's emotions continued to beat at him like moths, but they were quickly becoming overwhelmed by Gaster's persistence.

He released Sans's throat, trusting the hand constructs to hold him as he first pulled down his own trousers, and then Sans's shorts, knocking those ridiculous slippers off his feet as he got the shorts all the way off. As he kicked the offending clothing away he saw that Sans was practically dripping with arousal, and Gaster felt a spark of pride knowing that his intent was undeniable. He hooked his arm under Sans's pelvis, lifting him slightly to match his height.

"don't, i- _please-_ " Sans continued to beg weakly when his toes left the ground, his voice cracking as he realized there was no escape for him. 

The shaky, broken sob he made when Gaster began to prod at his entrance made Gaster throb with need, and he wanted nothing more than to plunge himself as deep as he could into that wet, waiting entrance.

So he did.

"Ga- ahh, ahh, ahh!" Sans screamed, twisting his skull to hide his crying against his arm as Gaster repeatedly forced himself in and out of the smaller monster. Gaster summoned another hand construct, instructing it to hook two fingers in Sans jaw and pull him back to where Gaster could see him properly.

He looked even better than the Sans on the screen had been. Scared, tears pouring down the sides of his face as he shook against the counter, forced to stare over his shoulder at Gaster, confused betrayal written like a beautiful accusation in his eyes. His body hiccoughed with the force of his sobs, repeatedly clenching around Gaster.

And yet, Gaster still wanted more.

He ignored Sans's frantic head shaking as he brought the Soul back to his mouth. Slowly, deliberately, he opened his jaw, setting Sans's Soul between his teeth, the sharp points of his canines pressing ever so slightly into the fragile surface.

Sans shrieked out in wordless horror, and Gaster groaned around the Soul in his mouth, closing his eyes in bliss at the pure, abject terror that was ripping through Sans like claws through paper.

Like teeth through a Soul.

He could really _feel_ that terror. Sans thought Gaster was going to kill him like this. As clearly as if he had spoken it aloud, Gaster could tell he was just waiting for the moment he knew was coming, where Gaster's intent would shift, where Gaster would bite down and-

As if thinking it made it true, Gaster couldn't stop himself from doing just that. He bit down, sucking on the Soul as he felt it discharge pure magic across his tongue. The noise Sans made was unparalleled, his whole body locking up as he screamed in pain. Gaster's grip on Sans's pelvis tightened, his rhythm falling to pure, mindless rutting until he came, crying out as he painted his release inside Sans's abused body.

For a moment Gaster knew nothing but bliss. When he came to, he was leaning over Sans, still pinned to the countertop beneath them. The hand constructs had vanished and Sans was trying to push him off, his chest heaving as he struggled to breathe. He must have let Sans's Soul fall from his mouth, and he sighed with relief that he wasn't leaning against an empty, dusty counter.

Gaster pulled back enough to slip free from Sans's magic, only for it to dispell immediately, leaving purple residue to leak from the inside of his pelvis, dripping wetly against the tiled floor. Checking his own clothes, Gaster was pleased to see that, other than being a bit rumpled, his clothing was perfect.

Releasing Sans's waist, Gaster let him go entirely and stepped back, quickly adjusting his clothes back to normal as Sans slumped to the floor. The sound bones collapsing against the tile sent a harsh jolt of guilt through him. 

Sans lifted his head to stare at him, and Gaster had to look away. He didn't want to see that broken expression. 

Except, he did. He really, really did. He wanted to photograph it, print a hundred copies and keep it close to warm the darkest part of his Soul.

Instead, he looked to the door, knowing that if he gave in, he would never leave.

"why?" Sans croaked, his voice soft as a breath.

"Because," Gaster answered.

 _Because I wanted to. Because you're beautiful. Because you're weak._

By the way Sans put his head in his hands and began to weakly cry again, Gaster believed his expression said everything his voice didn't. 

Without another word Gaster left the small lab and rapidly marched down the hallway to where the portal machine waited. He typed in his home coordinates, set the program to clear history in five minutes, and stepped through. 

On the other side, his own, true Sans was waiting for him, sitting in Gaster's chair with his ankles crossed on the desktop and mug of coffee in his hands.

"Heya, Doc," Sans greeted, not bothering to relinquish the chair or even lower his feet. He took a long sip from the mug as he watched the camera feeds. They were all from their own Underground, without a single AU to be seen. 

"So," Sans said slowly, like he was only curious, still keeping his eyes on the screen. "The Active AU Viewer feed is password protected now, huh? What's up with that?"

Gaster fought to keep his face as neutral as possible as he said, mostly truthfully, "I thought it would be better this way. I've recently discovered some unsettling universes, and I'd rather not burden you with the knowledge of what occurs in them."

Another long sip of coffee. "More unsettling than the universe where I'm an insane, homicidal cannibal?"

Gaster hesitated a moment too long, and Sans turned to face him directly. As Gaster stared into his sockets, he felt his sins crawling on his back.

"What happened, Gaster?"

"I-, well. It's very complicated," Gaster said, feeling sweat run down his brow. At some point, he had taken several steps back. "I do not wish to speak of it right now. Please, give me some time to process it and we will talk later."

"Oh, you bet we will," Sans said cryptically, turning back to the screen. "You go take your processing time. I'll be right here waiting for you."

From anyone else, that would have sounded like a threat. From Sans… well, it still sounded far too much like a threat. Gaster turned, heading for the door when Sans called out again.

"One more thing."

"Yes?" Gaster asked, not daring to turn around. He heard Sans take yet another long sip of coffee, and decided that, yes, that was definitely passive aggressive beverage drinking.

"It's nothing much," Sans said, his voice maddeningly opaque. "You've got a little something on your chin. Just thought you should know." 

"Alright, thank you, Sans," Gaster said. He left the room, feeling eyelights burning holes into his back for the whole short distance. 

Once he was out of sight, he reached to touch his face, encountering a wet trail on his cheek from the corner of his jaw. He dabbed at it with the edge of his sleeve.

Blue and silver.

He remembered the sound (other) Sans had made as his teeth sunk into the construct. He remembered the broken look in (other) Sans's eyes. He shuddered guiltily.

Gaster was screwed.


	2. Through Unshuttered Windows

**Summary for the Chapter:**

> Sans sure seems to know a lot. I wonder how he found out?
> 
> (Funny enough, this chapter is also canon for "Crossing an Unspoken Line", even if the second half of the last chapter is not. Yay, timelines!)

Only twenty minutes late, Sans signed in to his shift, relieved that Gaster wasn't standing by the clock waiting for him. 

He tried to be on time, he really did, but between taking care of Papyrus in the morning and his own apparent addiction to procrastination it rarely worked out. But, hey, maybe the doctor was running late and wouldn't notice, Sans thought, smirking at his own joke as he signed in. Glancing at the doctor's timesheet, Sans' smile cracked and fell as he was brought up short by what he read. 

It hadn't been filled out. Gaster hadn't signed in today. In fact, looking closer, it said he hadn't signed out last night either.

Sans frowned. He hadn't seen the doctor since lunch yesterday, where Gaster had seemed... extremely distracted. Which wasn't wholly unusual, he got that way sometimes after using the multiversal cameras, his attention pulled this way or that by the timelines and possibilities. But this…

Sans had greeted him by the coffee pot as normal, ready to make some quip about all work and no play, only to have Gaster flinch away, startling violently back at Sans' voice before staring at him with a hunger that looked a lot more desperate than a simple craving for instant ramen could account for. In that moment, Sans had the distinct impression of feeling exposed, as if he were some small animal standing before a predator. 

It had given him the wildest urge to run. Which was beyond ridiculous, of course. Gaster had been his friend and mentor for years and, except for Papyrus, there was no one else in the whole of the Underground he trusted more. So when Gaster had immediately excused himself and took off, practically fleeing, as if Sans was the one to fear, it left Sans only confused and staring out an empty doorway. It had been slightly unnerving to say the least, and Sans hadn't seen him since.

But not seeing Gaster for the rest of the day was another regular occurance that was hardly unusual, and certainly not a problem. They were both capable monsters, able to do their own work and finish tasks without another person breathing down their neck. At least usually, in Sans' case, and always, in Gaster's.

No, the part that was worrying was that Gaster was meticulous about paperwork in a way that Sans definitely wasn't. Gaster would never fail to sign out, unless he failed to leave. 

But even that happened, rarely enough. There was certainly no need for the sudden jolt of urgency that shot through Sans' Soul like he'd touched a live wire. No need at all for the panic that whispered that Gaster was gone. 

Gone. 

Sans took off at a quick almost jog to Gaster's office, his mind working hard to come up with excuses to override his unnecessary concern. There was no need to worry. Probably the doctor had just fallen asleep at his desk, too caught up in whatever he'd found yesterday to leave on time like a normal person. That had to be it.

First he checked Gaster's personal break room, in case he actually managed to make it to the bed inside. But the room was empty, just a chair, a bed, and a little table with the lamp. No scientist. Sans refused to feel discouraged. Gaster never took breaks here anyway.

He didn't pass another Soul on the way to Gaster's office, making the lab feel eerie, like he was some ghost left to wander the halls alone. He knew it was still pretty early, but Stars, shouldn't there be somebody here? He rounded the corner, pushing through the slightly ajar door labeled "W.D. Gaster" to let himself inside.

Gaster's office was empty. 

He walked around the room, searching the walls for answers, even checking behind the desk like Gaster might be hiding underneath it. Nothing but silence and shadows until Sans was forced to accept the conclusion that Gaster really wasn't in his office. The chill he'd felt earlier turned to cold fingers squeezing around his spine.

So many of the universes they'd found together were missing Gasters. A concerning majority of them, actually. The one time he'd managed to quietly ask another Sans about it he'd been quickly shut down with the words, "lab accident" and nothing more. Stars, he knew something was weird with the doctor yesterday, he should have checked on him! Why did he always just assume everything would be alright?

As Sans stared into the empty room, fighting his rising sense of panic, out of the corner of his socket he caught sight of someone standing in the doorway. He turned to find Alphys, nervously scanning around the room like she, too, was looking for a potentially hidden scientist as she rapidly scratched the back of one claw with the other. It was a anxious gesture that Sans wasn't particularly fond of. The last time he'd seen it was when she admitted to creating an evil toaster, and before that was the time she'd accidentally sent him a pdf file named, 'Sanster' instead of the schematics he'd asked for. 

~~He'd kept it, of course. For reference.~~

"G-good morning, S-Sans," she said, her discomfort making her stutter even worse than normal. "Have... have you s-seen Doctor Gaster y-yet?"

His Soul sank further in his chest. "No, I was about to ask you the same thing. I haven't seen him since yesterday."

"O-oh," she said, her head drooping slightly. "And, he was using the cameras yesterday... right?"

"Yeah, as far as I know he was on them all day," Sans said, rubbing the back of his skull as he tried to think.

"And…" she trailed off for a moment before continuing in a slightly higher pitch, "Y-you don't think he would use the machine alone, do you?"

"Without someone watching the Viewer? I doubt it, it'd be stupidly dangerous."

Alphys's fidgeting increased. "But… he might have?"

He met her eyes slowly, her tone setting off all kinds of alarm bells in his head. "Why? Is the Viewer active?"

Alphys shook her head. "N-no," she said, her voice dropping to a whisper.

"Then of course he wouldn't," Sans said. He wasn't sure who he was trying to convince. "It wouldn't just be dangerous, it'd be suicidal. What do the logs say?"

"N-nothing," she said, sounding hesitant as she grimaced through the word.

Sans breathed a small sigh of relief. On that front, no news was good news. He gave her a smile, and said, "Then it's fine-"

"Because they've been erased!" She interrupted with a small shout, only to pull back quickly, turning towards the wall. Her tail curled around her feet as she wrung her hands again. "And… and the Viewer itself has been password protected."

"What?!" Sans asked, reeling back. Only handful of monsters in the entire Lab had the administrative capabilities to even DO that, but only the three of them maintained access to the AU Viewer itself. If it wasn't him, and it wasn't her then... The mental alarm bells were clanging at full capacity now. "But… why? Do we have any information about what he was doing?"

"Nothing," Alphys confirmed, shaking her head again. Sans knew how much she hated being the bearer of bad news, and she looked ready to cry from it. "We don't even know how long he's been gone. Sans, oh g-god Sans, with the viewer down it- it could be ten seconds until he returns, or it c-could be ten y-years! Or n- nev-"

"Hold up Alphys!" Sans said, putting what he hoped was a comforting hand on her shoulder, despite the sharp prick of fear currently taking residence in his Soul. "We'll find him. He couldn't have deleted all the data, right? There's gotta be something left to check."

"I don't know!" She said, counting on her claws. "The c-coordinate history, the viewer's recorded feed and logs both, even the machine's b-back up snapshots for yesterday have all been manually erased!" 

Sans blinked dumbly for a moment. That was a surprising amount of trail covering. He went over the different record keeping methods they had, noticing that there was one thing she hadn't mentioned.

"What about the cctv in the camera room itself?"

The camera room served double duty, also housing the portal machine. While the camera was focused on the machine (all the better to spot any more interdimensional interlopers that might come through), it also had a good view of the cameras on the side.

Her eyes widened. "Oh! I didn't think of that!" She pulled her phone from her pocket and quickly began thumbing through her programs. Sans pulled out his own phone, but before he could connect Alphys gave a small cheer of victory. "Yes! It's still there!"

All the better, his phone was on 7% charge anyway. "Perfect, thanks Al. I'm going to head to the machine room and pull it up, at least that way we can figure out what he was looking at. Maybe that'll give us some clues. Hell, maybe I'll get lucky and spot the password."

"Good idea," she said, giving him a shaky but hopeful smile. "Ok, ok, and while you do that I-I'm going to try and run some more pingbacks against the machine o-or maybe some better recovery programs, and see if anything comes up. I'll l-let you know what I find, ok?"

"You got it, and I'll do the same," he said, giving her finger guns and a wink before taking off down the hallway.

The machine wasn't far, and it took all of three minutes to sit down, pull up the internal cctv directory (thankfully not password protected), find the recording from yesterday morning and load it in. The monitor obediently filled with yesterday's video of the machine room, Gaster sitting at the same chair Sans was now in himself. Glancing over his shoulder, he peered up at the little camera in the corner, giving it a thumbs up in silent thank you. 

There was no audio, but hopefully they wouldn't need any. Sans increased the window size to only show Gaster and the monitors, which also made it easier to see the feeds he'd been going over, then hit the 4x speed button and began to watch. It was a lot of nothing special, watching Gaster's back while he drank coffee as he reviewed the footage from older AU's they'd found. Gaster writing notes. Gaster leaving to get more coffee. He sped it up to 8x. More notes. More coffee. Then he realized the screen in the recording had gone black and he paused the image. Gaster had stood up and was leaving the room, a look of concerned horror on his face. 

Oh, shit.

Quickly Sans backed up the video by ten minutes and began to play. It seemed harmless enough, Gaster had switched from old recordings to 'current' feeds, shifting casually between different AUs. Then he saw Gaster alert on a more staticky camera image. It had a slightly distorted quality that only came from a new universe on the Active AU Viewer feed, before the machine could properly compensate for the universe's unique frequency. He watched Gaster explore the lab on the screen for a minute before clipping the camera through a random door.

Sans felt his Soul drop as he saw himself sitting on an exam table. He… didn't look good. An experimentation universe, and worse than most, based on the hollow eyed expression the other him wore. 

There was a flurry of motion on the camera as Gaster started taking notes again, an angry set to his shoulders. Sans smiled at that. Good ol' Gaster, a softy when it came to the more unfriendly universes. It had taken Sans a long time to accept that he couldn't help everyone, but he was a realist. There were just too many. Apparently Gaster still wanted to intervene, and on his behalf too. It was sweet.

And then Gaster froze, staring at the screen. Sans followed his gaze, only to freeze himself. It was like someone reached into the darkest part of his skull, found one of his dirtiest, most shameful fantasies and decided to play it out on screen. Gaster, looking larger than life, precise and put together, standing over his bare bones...

But that wasn't excited fear written across his face. That was a look that said this Sans sorely, and clearly didn't have, a safe word. He didn't want this.

It only got worse as, while he watched, the Sans on the screen _pulled out his Soul_. Sans' own magic began to buzz along his bones, helpfully reminding him of all the times he imagined what Gaster's touch on his body, on his Soul would feel like. And that expression on the other Gaster's face… By the time the other doctor opened his pants, Sans had forgotten how to breathe correctly, leaving him flustered and disturbed, but unable to turn away.

It took far too long for Sans to realize that his own Gaster wasn't turning away either. The doctor was still onscreen, watching, the same as he was. Shouldn't Gaster be horrified? Why hadn't he turned it off? Why were they both still watching? With his back to the camera, Sans had no way to read his face to know what he was thinking.

They remained like that, both staring, frozen, as the Sans on the screen was mercilessly used. Sans couldn't take his eyes off the Soul in the other's fist... 

When he saw Gaster move again, it was to press his wrist into his teeth, and Sans had his remaining breath knocked out of him when he realized the doctor's other hand was in his pants. The doctor shuddered, hard, very clearly finishing himself off to the sight of Sans' onscreen rape.

Sans could do nothing but stare in mute disbelief as the doctor turned off the camera and fled the room. His magic pulsed in his bones and he licked his teeth, not exactly sure when his tongue had formed. It wasn't the only thing he'd inadvertently summoned, either. Wow. He ached to touch himself but, apparently unlike Gaster, he knew better than to box the clown while on camera.

This was fucked up. He'd already known that he was fucked up, but to find out that Gaster was apparently fucked up too...?

And that was the part he couldn't believe. It was no big surprise to Sans to realize once again that he had issues, considering some of the fantasies he'd had ~~and would never admit to outloud~~ , but had Gaster, the kind, genius he'd known for years, really gotten off to that? To vicariously (and, beyond a doubt, sadistically) fucking Sans?

And it wasn't like it had been one of those Felled or Swapped versions of Gaster either. No, that had been, without a doubt, a Gaster just. like. his. own.

Well, Sans thought, sitting back in the chair, that was unexpected. With a sudden flash of inspiration, Sans remembered the note Gaster had been writing. He pushed back, searching all over the desk, before finally spotting it on the ground, half hidden near the wall.

It was a set of coordinates. Most of a set, anyway. The camera feed wasn't nearly good enough to read the remaining digits, but he knew Alphys could find them through a little trial and error if he asked. If this was where Gaster went, the quicker they opened the portal to it the better.

Pulling his phone out, he called Alphys. "Hey, got some coordinate digits." He waited until he heard the sound of rustling papers stop, and then he read them out.

"Ok," Alphys said. "What's the rest?"

"Dunno, they didn't all get written down. But I think this might be where the doc went. Can you pull up the rest?"

"Probably, the data crawler should be able to snag the match, but we won't be able to see what kind of universe it is with the Viewer down."

"I saw it on the camera. It's an experimentation universe and, well, let's just say I'm glad I'm not there."

There was undisguised horror in her voice as she exclaimed, "An ex-? O-oh no... Not the ch-children one again?"

"No," Sans said with a grimace, only to cover it by moving back to the cameras, the reflex to deflect strong despite the fact she couldn't see him. "It's different, more like ours, I think, except… heh, well, I'd _really_ rather not say."

"I… think I understand," she said, her voice going soft. Sans didn't think that was exactly true, but he wasn't about to explain. "I'll do what I can w-with the coordinates."

"Thanks Al," he said, forcing a smile back into his voice. "I'm gonna keep looking for more clues."

"I'll l-let you know what I find," she said. "W-we'll find him, Sans. I know we will. Gaster wouldn't give up on us, and we c-can't give up on him either."

"Yeah." It was hard not to think of all the Gaster-less universes, and the idea was crushing. But one detail was different, and he clutched to it like a lifeline. Where Gaster ceased to exist, Alphys forgot his name. A spark of hope rekindled as he said, "We will. Even if we have to go drag him back ourselves."

He hung up and went back to the camera, saving the feed to his personal storage with the flimsy pretense of saving it for redundancy. Not just because he wanted to explore every facet of Gaster's body language, watch him shudder in the chair. Stars, he was a creep, but Gaster really shouldn't be doing that sort of thing at work. Plus, there was probably good information to find on the clip of the Viewer roaming the foreign universe.

For now, there was more video to watch. He drew the camera focus back to show the entire room.

While the camera had a decent view of the monitors and the viewer, it was the machine that it was mainly focused on. If Gaster went through there, he'd see it.

~~~

His fears had been true. Gaster had used the machine. Sans had seen him exploring their current universe, clearly checking that Sans was distracted by his work downstairs, before he'd locked everything and activated the portal.

Sans jumped as his phone buzzed on the desk beside him. He'd had the forsight to actually plug it in to charge for once, and promptly forgot about it. Picking it up, he asked, "Heya Al, any luck with the digits?"

"Yes," she said simply. "I can o-open to that universe, but, for some reason the machine doesn't r-recognize it, only responding back with the camera logs."

"It's probably got something to do with the memory wipe," Sans reasoned. "I saw Gaster use the machine on camera, I was just about to call you."

"S-so he really did leave."

"Yeah." Sans gave a frustrated sigh, unplugging his phone so that he could pace the room. "I haven't had any success on getting into the Viewer. Any chance you managed to crack the password?"

"N-no," she said with an irritated hiss of her own. "Gaster's passwords are notoriously complex."

"Don't I know it. But… what if…" He was waving a hand in the air as he talked, he realized. Likely something he picked up from Gaster. "What if we don't need it. What if there was a workaround?" 

"A workaround?" She asked, hope growing in her voice.

"It's just a theory, but…" Sans walked over to the machine, looking it over as he asked, "Who says the cameras have to watch the visiting universe?"

"The…? Oh! That's… that's a good idea! If our phones can connect to the cameras here we can hold the connection stable as long as we keep and eye on them!"

"Wait, what do you mean, 'our phones'?"

She let out a laugh that sounded a little shrill. "I'm not going to let you explore an ex-exp- a bad universe alone. That's just asking for trouble and y-you know it." There was the sound of shuffling, and she said, "Don't do anything r-rash, I'll be right there."

"Ok," he said, opening the startup sequence for the machine. "But I'm not gonna wait for long."


End file.
